1. Field of the Invention
This invention relates to a process for the improved recovery of soluble coal products from a continuous coal deashing process.
2. Description of the Prior Art
Various coal deashing processes have been developed in the past wherein coal has been treated with one or more solvents and processed to separate the resulting insoluble coal products from the soluble coal products.
U.S. Pat. Nos. 3,607,716 and 3,607,717, assigned to the same assignee as the present invention, describe processes wherein coal liquefaction products are contacted with a deashing solvent and the resulting mixture is introduced into a separation zone maintained at elevated temperature and pressure and separated into a heavy phase containing the insoluble coal products and a light phase containing the soluble coal products. When the separation is effected under the proper conditions of temperature and pressure, the heavy phase is easily flowable from the separation zone for withdrawal therefrom. However, if conditions are adjusted to increase the yield of soluble coal products recovered as the light phase beyond a certain extent, the heavy phase is no longer easily flowable. When attempts are made to remove such heavy phase (even though it is fluid-like) the withdrawal conduit or the downstream processing apparatus may become plugged by solidified heavy phase material. Once the fluid-like heavy phase solidifies within the process apparatus, it can only be returned to its fluid-like condition by the introduction of soluble coal products or other high-boiling aromatic materials. Such use of the soluble coal products necessarily results in a substantially lower net recovery of deashed soluble coal products from the process.
U.S. Pat. Nos. 3,947,346 and 3,954,595, describe processes wherein coal liquefaction products are contacted with a promoter liquid to separate insoluble coal products. The mixture of coal liquefaction products and promoter liquid is introduced into a gravity settler wherein the insoluble coal products separate as an underflow that is withdrawn and stripped to recover a portion of the remaining soluble coal products. Those patents disclose that to maintain the stripped solid-containing stream flowable, the stream should contain sufficient soluble coal to provide a benzene solubles content of at least 35 percent. Normally, the benzene solubles content of the stripped solid-containing stream is in the range of from about 40 to 60 percent.
It is desirable to provide a process by which coal liquefaction products can be treated to separate insoluble coal products from the soluble coal products with a minimum loss of valuable soluble coal products while still maintaining the stream in a flowable condition.